In cases where it is desired to use mixing heads of this kind for producing plastics articles with different properties, it is often necessary to change the components and/or to inject them into the mixing chamber under different pressures. The injection pressure is governed by the size of the injection openings. If, in conventional slide type mixing heads, it is desired to change this pressure, at least one of the slides has to be taken out and replaced by another slide with an injection opening having a different cross-sectional area. Alternatively, a higher pressure has to be built up by increasing the output of the pumps delivering the components.
An object of the present invention is to provide a mixing head which enables the pressures under which the components are injected to be altered in stages without any need to replace a slide.